The trend in the automotive industry to simultaneously move to higher efficiency, hotter-running engines and lower viscosity lubricants for fuel economy has led to durability challenges in both passenger car and heavy duty diesel engine applications. One approach taken to enhance the durability of these engines has been to incorporate boron into the lubricant. Boron-containing fluids have a history of exhibiting oxidation inhibition and anti-wear properties in a range of environments (U.S. Pat. Nos. 4,724,099, 3,224,971, 3,185,644, 4,756,842, 4,657,686, 3,014,061, 2,813,830). Boron can be introduced in significant amounts via small molecules (e.g. boron esters, EP0089844, GB434626, U.S. Pat. Nos. 3,347,793, 3,509,054, FR1203698), however, incorporation of these materials into lubricants can cause adverse side effects, such as corrosion issues and phase separation. Boron can also be introduced via additive carriers such as dispersants or detergents (U.S. Pat. No. 3,087,936, GB1086692, U.S. Pat. Nos. 3,829,381, 3,928,216). However, the amount of boron introduced by such carriers needs to be matched with the amount of carrier. For high boron concentrations, the required large amount of carrier (associated dispersant or detergent) can lead to an inordinately high viscometric contribution, which adversely impacts base stock flexibility. A solution to this problem would be to prepare a boron carrier, specifically a borated dispersant concentrate, with very high boron content that could be used broadly in a range of applications without significantly impacting fluid viscometrics or additive treat rates.
Historically, such borated dispersant concentrates are known where the total nitrogen to boron molar ratio is in the range 4:1-1:2 (U.S. Pat. No. 5,583,099; 1:1-1:1.25 in examples) with preferred ratios containing an excess of nitrogen or being close to stoichiometric (e.g. 2:1-1:1). Borated dispersant concentrates are typically prepared by reacting boric acid with a range of dispersant types while sweeping out water. It is believed that during the boration process, boric acid dehydrates to cyclic metaboric acid (Structure I, shown below) leading to the evolution of water. The oil-insoluble metaboric acid is solubilized in the dispersant concentrate by interaction with the basic nitrogens on the dispersant. The products of the invention disclosed in U.S. Pat. No. 5,583,099 are prepared by reacting boric acid with a dispersant compound containing an amide, imide or Mannich base group having present at least one amine group or salt thereof, in the presence of a protic compound, in a weight ratio to boric acid of at least about 1:2.

Highly borated dispersant concentrates are described where the boron to total nitrogen weight ratio is in the range of about 0.2 to about 65 (EP0499384A1); corresponding to a nitrogen to boron molar ratio of about 0.15 to about 50.3. The polybutene of the succinimide had an Mn within the range of 900 to 3000 daltons, with a most preferred range of 1200 to 2300 daltons. The boron-containing moiety of this borated succinimide was a boron oxide (BxOy)z wherein x and y are 1 to 3 and z is 2 to 56. The process used to incorporate the boron utilized a very high temperature (170 to 260° C.; preferably 182 to 218° C., e.g., 182 to 193° C. in order to completely dehydrate the orthoboric acid to boron oxide (B2O3, Structure II). The eliminated water collected using a Dean and Stark apparatus corresponded to more than 1.5 mole of water per mole of boric acid charged, which supports the position that boron is present in the product in the form of boron oxide. Using this approach, the efficiency of the boron incorporation is relatively low (about 50 to 90%), resulting in compositions having significant amounts of sediment that has to be removed using filtration.
